1. Field of the Invention
The present invention relates generally to drilling well bores through the earth with a rotary drill bit. More specifically, the present invention relates to the structure and use of a nozzle employed to direct and control the flow of drilling fluids exiting from a drill bit.
2. Brief Description of the Prior Art Background of the Invention
Wells drilled in the earth are commonly formed with the use of a rotating drill bit positioned at the bottom of a tubular drill string. Rotation of the bit progressively cuts away the earthen formations engaged by the bit face to form a well bore. Drilling fluids pumped down the drill string to the bit exit the bit face through nozzles strategically disposed in the bit body. The fluid is used to clean, cool and lubricate the bit and assist in breaking away the formation. The fluid also serves to maintain pressure equilibrium within the well bore and carry formation cuttings back to the well surface.
Proper operation of the bit requires that the drilling fluid exit the bit with a flow pattern and velocity that are suited for a given bit design, as well as the anticipated well drilling environment. Nozzles carried in the drill bit function to direct and control the flow path and the pattern and velocity of the drilling fluids exiting the bit.
Drill bit bodies are customarily provided with internally threaded nozzle receptacles that can receive externally threaded nozzle bodies having a desired jetting characteristic. With conventional, non-directional nozzle bodies, the final angular orientation of the nozzle body once seated in the bit receptacle does not affect the proper operation of the fluid jetting action of the nozzle. However, where the fluid is to leave the nozzle at an angle relative to the nozzle axis, the final angular disposition of the nozzle within the receptacle determines the direction of flow of the exiting fluid over the bit body.
A nozzle having a directional exit flow pattern must remain firmly anchored within the nozzle receptacle after its installation so that it does not move axially or angularly during use. One technique for preventing such movement is to cement the nozzle within the receptacle at the desired axial and angular position. This technique suffers various shortcomings including the possible failure of the cement to properly retain the nozzle in place as well as the difficulty encountered in removing and replacing the nozzle after it has been cemented within the receptacle.
Proper final orientation of the nozzle in a threaded receptacle can be achieved by exactly matching the external threaded surface of the nozzle to that of the thread pattern in the receptacle such that the nozzle is seated and can no longer be rotated at the precise orientation producing the desired exit flow direction. One of the problems encountered in attempting to time the nozzle thread pattern to that of the receptacle threads relates to the need to form a precisely developed thread on the external surface of the nozzle body. The nozzle is desirably constructed from an extremely hard material such as tungsten carbide that is very difficult to machine. For this reason, nozzle assemblies are frequently constructed as multi-part components that include a tungsten carbide body and a surrounding steel sleeve with the threads machined into the softer steel material of the sleeve.
In some of the prior art designs, the sleeve is brazed or otherwise bonded to the nozzle body to prevent relative rotation between the two components. This technique can permit the nozzle and receptacle thread patterns to be timed with the nozzle flow direction so that the final seated position of the nozzle produces the desired orientation of the exit flow path from the bit. Use of this technique requires that each nozzle and sleeve assembly be bonded to be used in a specific matching receptacle. The technique is also limiting in that it is necessary to perform a bonding step immediately before the nozzle is installed, making field installations complicated and difficult. The use of shims to control the final seated position of the nozzle is also impressive and difficult to implement.
Some prior art nozzle bodies are formed by molding tungsten carbide to provide a single material body with an externally threaded surface. Creation of a precisely molded thread pattern that will meet with the internal threads of a specific nozzle receptacle such the final, seated position of the nozzle in the receptacle results in a predetermined orientation of the directional nozzle is also difficult to achieve. In general, techniques that require matching nozzle and receptacle threads in single body or bonded nozzle construction to determine final, seated orientation of a directional nozzle relative to the bit body are difficult and time-consuming.
The prior art includes a multiple-piece nozzle design in which an externally threaded, split sleeve closely surrounds a cylindrical nozzle body. The nozzle body may be angularly positioned within the sleeve before the assembly is placed in the receptacle so that the nozzle body is properly oriented when the nozzle and sleeve assembly is seated. This prior art design, described in U.S. Pat. No. 4,533,005 to Morrison, employs frictional force between the engaged, smooth internal cylindrical surfaces of the sleeve and nozzle body to hold the nozzle orientation once the nozzle has been seated in the receptacle. A specially configured tool is required to seat and extract the nozzle. The tool includes axially extending fingers that simultaneously engage aligned openings in the nozzle body and the threaded sleeve so that the two components of the nozzle assembly may be rotated as a unit. The fixed angular position of the nozzle is determined by rotating the nozzle within the sleeve to a selected angular position that will result in the desired final nozzle orientation when the sleeve is firmly seated within the nozzle receptacle.
While the Morrison prior art design offers improvements over the technique of cementing the nozzle within the receptacle, or attempting to match nozzle and receptacle thread patterns, the anchored nozzle of the Morrison design is susceptible to rotation during use because of the reliance on frictional engagement alone to prevent such rotation. Retaining the proper orientation of the nozzle body within the sleeve before the assembly is finally seated can also be difficult because of the slippage that may occur before the assembly is fully seated.
U.S. Pat. No. 4,794,995 to Matson describes a directional nozzle assembly that is held in place by an externally threaded sleeve. As with the Morrison design, the Matson design relies on frictional engagement between the sleeve and the nozzle body to prevent rotation of the nozzle within the sleeve.
A prior art nozzle design that employs a mechanical interlock rather than frictional engagement to prevent nozzle rotation is described in U.S. Pat. No. 4,776,412 to Thompson. The design employs a specially shaped bit receptacle having circumferentially spaced slots that mate with corresponding spaced nibs formed at the base of the nozzle body. A specially configured drive tool is employed to seat an externally threaded sleeve into the threaded receptacle and over the cylindrical nozzle body to hold the nozzle in the receptacle. Rotation of the nozzle is prevented by the interlocking engagement of the bit recess slots and the nozzle nibs. While the design is effective in preventing rotation of the installed nozzle, it is complex, requires a relatively large number of separate construction components, is difficult to build, and requires the use of a special drive tool.